You are definitely helping! Neither of us can do anything to change how these features work but getting a better understanding of what can be done without causing a mess or a crash is as helpful as one could be.
It really is a shame that is requires so much work to do what should be simple tasks just like changing the image used to the Genre. I think currently it uses the Artist that has the most albums tagged with that Genre, but that does not mean they represent that genre the best.
It is interesting that your Discovery page fixed itself after a little bit of time. I was having the opposite thing happen where I would get my Genres page with no missing images, but then the next morning two or three new Genres would pop up with no images. So it became never ending for me. I am glad it is working in your favor though. I am also hopeful that a lot of these things are just errors in their server or something that they can fix on their end.
I have been searching for the best way to organize genres and determine which genres should be sub-genres and which should be top level and so far the best site I have found it. https://musicmap.info is what I have been using as a loose reference.
Hopefully one of us will hear something soon!